U.S. patent application number 09/953485 was filed with the patent office on 2002-04-11 for system and method for determining location and tissue contact of an implantable medical device within a body.
Invention is credited to Iaizzo, Paul A., Laske, Timothy G..
Application Number | 20020042632 09/953485 |
Document ID | / |
Family ID | 27398507 |
Filed Date | 2002-04-11 |
United States Patent
Application |
20020042632 |
Kind Code |
A1 |
Iaizzo, Paul A. ; et
al. |
April 11, 2002 |
System and method for determining location and tissue contact of an
implantable medical device within a body
Abstract
The current invention provides an improved system for monitoring
status of an IMD within a body. The system includes a device such
as a lead, guidewire, stylet, catheter, or other IMD carrying a
device such as a microphone for detecting acoustic signals in the
body. The IMD is coupled to an amplifier device which generates an
audible signal that may be utilized to determine status associated
with the IMD, including location and tissue-contact data. A
processing circuit may further be provided to aid in the analysis
of the acoustic data.
Inventors: |
Iaizzo, Paul A.; (White Bear
Lake, MN) ; Laske, Timothy G.; (Shoreview,
MN) |
Correspondence
Address: |
Beth L. McMahon
Medtronic, Inc., MS 301
7000 Central Avenue NE
Minneapolis
MN
55432
US
|
Family ID: |
27398507 |
Appl. No.: |
09/953485 |
Filed: |
September 14, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60234058 |
Sep 20, 2000 |
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60256630 |
Dec 18, 2000 |
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Current U.S.
Class: |
607/27 |
Current CPC
Class: |
A61B 8/0833 20130101;
A61B 5/06 20130101; A61N 1/056 20130101 |
Class at
Publication: |
607/27 |
International
Class: |
A61N 001/36 |
Claims
What is claimed is:
1. A system for monitoring an implantable medical device (IMD)
within a body, comprising: a first circuit to receive an electrical
signal that is representative of an acoustic signal existing within
a body; and a second circuit coupled to the first circuit to
provide an audible signal from the received electrical signal for
use in determining status associated with the IMD.
2. The system of claim 1, wherein the first circuit includes an
amplifier circuit coupled to a filter circuit.
3. The system of claim 1, and further including a processing
circuit to receive the electrical signal, and to utilize the
electrical signal to generate an indication of IMD status.
4. The system of claim 3, wherein the processing circuit includes
means for comparing the received electrical signal to predetermined
acoustic patterns to generate an indication of IMD status.
5. The system of claim 4, and further including an output device
coupled to receive the indication of IMD status from the processing
circuit.
6. The system of claim 5, wherein the processing circuit includes
means for generating a virtual image of the IMD on the output
device.
7. The system of claim 4, wherein the processing circuit includes
means for analyzing signals received from at least one additional
physiological sensor for use in generating an indication of IMD
status.
8. The system of claim 4, wherein the processing circuit includes
means for determining approximate location of the IMD.
9. The system of claim 8, wherein the processing circuit includes
means for determining tissue contact associated with the IMD.
10. An implantable medical device (IMD) within a patient,
comprising: a measurement device to sense an acoustic signal; a
circuit coupled to the measurement device to determine, based on
the acoustic signal, status indicative of a patient condition or
status associated with the IMD.
11. The IMD of claim 10, wherein the IMD includes a switch to
selectively coupled the measurement device to the circuit.
12. The IMD of claim 10, wherein the circuit includes a processing
circuit to receive an indication of the acoustic signal and to
thereby generate status indicative of the patient condition or the
status associated with the IMD
13. The IMD of claim 12, wherein the processing circuit includes
means for determining contact between a portion of the IMD and
tissue from the acoustic signal.
14. A system for use in providing therapy to a body, comprising: an
implantable medical device (IMD) including a acoustic measurement
device to receive acoustic waves transmitted within the body; and a
second device coupled to the IMD to receive an indication of the
acoustic waves, and to thereby provide data indicative of status
associated with the IMD.
15. The system of claim 14, wherein the IMD includes at least one
electrode and a switch to selectively couple either the acoustic
measurement device or the at least one electrode to the second
device.
16. The system of claim 14, wherein the IMD is selected from the
group consisting of a catheter, a medical lead, a guidewire, and a
stylet.
17. The system of claim 14, wherein the second device includes a
processing circuit to process the indication of the acoustic waves,
and to thereby generate data indicative of status associated with
the IMD.
18. The system of claim 14, wherein the second device is a second
implantable medical device.
19. The system of claim 18, wherein the second device includes a
communication circuit to transmit the data indicative of status to
an external device.
20. The system of claim 14, wherein the second device is a device
located outside the body.
21. The system of claim 20, wherein the second device includes an
output device to provide the data indicative of the status to a
user.
22. The system of claim 21, wherein the second device is a display
monitor to display a determined location of the IMD within the
body.
23. A method of monitoring an implantable medical device (IMD)
including an acoustic measurement device within a body, comprising
the steps of: a.) utilizing the acoustic measurement device to
sense acoustic signals within the body; and b.) determining status
associated with the IMD based on an indication of the acoustic
signals.
24. The method of claim 23, wherein step b.) includes determining a
location of the acoustic measurement device within the body.
25. The method of claim 23, wherein step b.) includes determining a
degree of tissue contact between a portion of the IMD and the
body.
26. The method of claim 23, wherein step b.) includes assessing a
condition of the body based on the indication of the acoustic
signals.
27. The method of claim 26, and further including providing a
warning following assessing of the condition of the body.
28. The method of claim 24, wherein the IMD includes at least one
additional sensor for sensing physiological signals, and further
including utilizing the sensed physiological signals to gain
additional status associated with the IMD.
29. The method of claim 28, and further including utilizing the
sensed physiological signals to confirm the location of the
acoustic measurement device within the body.
30. The method of claim 23, and further including providing the
status to an output device.
31. The method of claim 23, and further including creating an image
of the IMD on a display device.
32. The method of claim 23, wherein step b.) includes comparing the
indication of the acoustic signals to predetermined acoustic
patterns to determine the status.
33. The method of claim 32, wherein the acoustic patterns are
tailored to characteristics of the body.
34. The method of claim 23, wherein the IMD includes a switch
coupled to the acoustic measurement device, and further including
the step of selectively configuring the switch so that the acoustic
measurement device may be utilized to determine the status.
Description
RELATED APPLICATIONS
[0001] This application claims priority to provisionally-filed
patent application serial No. 60/234,058 filed Sep. 20, 2000, and
further to provisionally-filed patent application serial No.
60/256,630 filed Dec. 18, 2000, which is incorporated herein by
reference in its entirety.
FIELD
[0002] This invention relates generally to a system and method for
placing leads within a body; and more particular, relates to the
use of audio signals for determining lead location and for
assessing the level of tissue contact achieved by one or more
devices carried on the lead.
BACKGROUND OF THE INVENTION
[0003] Implantable medical electrical leads have long been employed
in the fields of cardiac stimulation and monitoring. For example,
leads are generally employed to deliver electrical stimulation for
cardiac pacing and cardioversion/defibrillation applications. In
these applications, endocardial leads are placed through a
transvenous route to locate one or more sensing and/or stimulation
electrodes in a desired location within a heart chamber or
interconnecting vasculature. To provide effective therapy,
electrodes carried at the lead distal end need to be accurately
positioned at a predetermined location against the endocardium or
within the myocardium. The lead distal tip is then generally
affixed by a passive or active means to the tissue to maintain the
desired locations.
[0004] It is often difficult to determine whether a lead has been
properly positioned and adequate tissue contact has been achieved.
In some instances, catheters and leads are utilized that include
materials that will allow for visualization with fluoroscopy.
Additionally, fluoro-visible dyes may be injected into the cardiac
chambers and venous anatomy so that the chambers of the heart and
the related vasculature are visible using a fluoroscopic device.
This procedure, sometimes referred to as a "venogram", allows the
surgeon to locate a precise site and achieve proper electrode
placement when performing an implant procedure.
[0005] Although the use of fluoro visible media is viable in some
instances, this process has several disadvantages. First, some
patients have adverse physical reactions when exposed to the fluoro
visible dye used to obtain a venogram. Moreover, obtaining the
venogram exposes the patient and clinicians to radiation.
Additionally, a fluoroscope of the type needed for obtaining the
fluoro-visible image may not be available. Finally, obtaining the
venogram adds additional steps to the implant procedure,
lengthening the time required to complete the procedure and
increasing the risk of infection and complications to the
patient.
[0006] What is needed, therefore, is an alternative system and
method for placing, and otherwise monitoring the status of, an
implantable medical device within the vascular system of the body
without the need to inject a fluoro visible media into the
body.
SUMMARY OF THE INVENTION
[0007] The current invention provides an improved system for
monitoring status of an IMD within a body. The system includes a
device such as a lead, guidewire, stylet, catheter, or other IMD
carrying a device such as a microphone for detecting acoustic
signals in the body. The IMD is coupled to an amplifier device
which, in one embodiment, may be provided by a stand-alone device
or included within an external programmer. An electrical
representation of the measured acoustic signal is provided by the
IMD to the amplifier device so that an audible signal may be
generated by the amplifier device. A trained user can utilize the
pitch and other characteristics of the audible signal to determine
status associated with the IMD. Because unique patterns are
associated with the acoustic signals that may be measured at
distinct points within the cardiovascular system, the pitch of the
audible signal may be used to determine the location of the
acoustic measuring device, and thus, the IMD, within the body.
Other information may be gained from the audible signal, including
the extent of any contact between the IMD and tissue, and/or the
extent of fixation of the IMD to tissue.
[0008] In one embodiment of the invention, the amplifier device
includes a processing circuit to analyze the audible signal. For
example, the processing circuit may compare the sensed audible
signals to stored patterns. This comparison may then be used to
determine IMD status, including location and tissue contact data.
The processing circuit may provide this status information to an
output device such as a printer or display monitor. According to
one aspect of the invention, a virtual image of the IMD within the
body may be generated using the status information.
[0009] The IMD of the current invention may include a switch
mechanism. This switch mechanism may be used to selectively couple
signals generated by the acoustic measurement device to a connector
of the IMD during an implant procedure. This switch is
re-configured during normal IMD operation so that other sensing
devices such as electrodes are coupled to the connector. Use of
this type of switching mechanism allows a standard connector, or
alternatively, a non-standard connector having minimal connector
contacts, to be utilized by the IMD.
[0010] The IMD may further include additional physiological sensors
such as pressure, temperature, flow velocity, flow acceleration,
and electrical activity sensors to provide additional physiological
signals measured within the cardiovascular system to the amplifier
device. This data may be utilized to confirm, or to further
enhance, the status data that is generated using the acoustic
signals.
[0011] In one embodiment of the invention, the amplifier device is
included within a second IMD such as a pacemaker,
cardioverter/defibrilla- tor, drug pump, or any other implantable
medical device rather than an external device. Periodic acoustic
measurements are provided by the first IMD, which may be a lead, to
the second IMD. This may involve configuring an electronic switch
included within the lead to make the signals available to the
second IMD. These acoustic signals may then be used by the second
IMD to detect dislodgement or detachment of the first IMD, or to
analyze a patient's condition. In response to the sensing of a
predetermined patient condition, the second IMD may issue an alert
or modify therapy delivery. The acoustic data may further be stored
as trend data that may be used by a clinician in evaluating
long-term patient condition. Other aspects of the current invention
will become apparent to those skilled in the art from the drawings
and accompanying description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a diagram illustrating an implantable medical
device (IMD) system implanted within a body of a patient.
[0013] FIG. 2A is a side view of one embodiment of a lead that may
carry a microphone or another similar device for detecting sound
waves.
[0014] FIG. 2B is a side view of alternative embodiment of a lead
for use with the current invention.
[0015] FIG. 2C is an end view of yet another embodiment of a distal
end of a lead for use with the current invention.
[0016] FIG. 2D is a side cutaway view of the embodiment of FIG.
2C.
[0017] FIG. 3 is a block diagram of a system that utilizes sound
waves to aid in the positioning of a lead within a patient's body
during an implantation procedure.
[0018] FIG. 4 is a block diagram of an implantable medical device
(IMD) as may be used with the current inventive lead system.
[0019] FIG. 5A is a side view of an exemplary deflectable guide
catheter 200 as may be employed with the current invention.
[0020] FIG. 5B is a perspective view of an exemplary steerable
stylet that may be employed with the current invention.
[0021] FIG. 6 is a flowchart of an exemplary process of obtaining
status associated with an implantable medical device according to
the current invention.
[0022] FIG. 7 is a flowchart of an exemplary process of utilizing
the current invention to monitor long-term status of IMD implanted
within a patient.
DETAILED DESCRIPTION OF THE INVENTION
[0023] FIG. 1 is a diagram illustrating an implantable medical
device (IMD) system implanted within a body of a patient. The
system includes a device for detecting sound waves shown as
microphone 5. The microphone may be attached to, or integrally
formed as a component of, lead 14, or another type of IMD, as will
be discussed below. In the case of a lead, the lead may be unipolar
or bipolar, and may be adapted to operate in cooperation with a
wide variety of implantable medical devices.
[0024] Lead 14 is positioned in heart 16 of patient 10, and is
attached to IMD 11, shown implanted in the upper right chest of
patient 10. The lead 14 may include any of the passive or active
fixation mechanisms known in the art. For example, lead distal tip
27 may include a tined tip. Lead may further include one or more
electrodes, such as a tip electrode 26. Tip electrode senses
electrical signals attendant to the depolarization and
repolarization of heart 16, and may also transmit pacing pulses for
causing depolarization of cardiac tissue in the vicinity of the
electrode. Lead may further include a ring electrode, one or more
high-voltage electrodes, and/or one or more additional sensors such
as sensor 15. The use of these additional sensors is discussed
further below.
[0025] IMD 11 may be an implantable cardiac pacemaker, such as of
the types disclosed in U.S. Pat. No. 5,158,078 to Bennett et al.,
U.S. Pat. No. 5,312,453 to Shelton et al., or U.S. Pat. No.
5,144,949 to Olson, hereby incorporated herein by reference in
their respective entireties. IMD 11 may also be a
pacemaker-cardioverter-defibrillator (PCD), such as any of those
disclosed in U.S. Pat. No. 5,545,186 to Olson et al., U.S. Pat. No.
5,354,316 to Keimel, U.S. Pat. No. 5,314,430 to Bardy, U.S. Pat.
No. 5,131,388 to Pless, or U.S. Pat. No. 4,821,723 to Baker et al.
At least some of the devices disclosed in the foregoing patents may
be employed in conjunction with the present invention. In yet
another embodiment, IMD 11 may be an implantable nerve stimulator
or muscle stimulator, such as those disclosed in U.S. Pat. No.
5,199,428 to Obel et al., U.S. Pat. No. 5,207, 218 to Carpentier et
al., or U.S. Pat. No. 5,330,507 to Schwartz, or an implantable
monitoring device, such as that disclosed in U.S. Pat. No.
5,331,966 issued to Bennet et al. The IMD may alternatively be a
hemodynamic monitor or a drug pump. In general, IMD 11 is encased
in a hermetically-sealed enclosure that may include various circuit
elements to be discussed in more detail below.
[0026] As discussed above, lead 14 is shown to include microphone
5. This microphone may be any type of microphone suitable for
implantation within a living body. For example, implantable
microphones used with implantable electromagnetic hearing
transducers may be employed, as described in U.S. Pat. Nos.
5,554,096 and 5,456,654 to Ball, and U.S. Pat. No. 5,085,628 to
Engebretson et al. Additional exemplary microphone designs are
disclosed by Iwata in U.S. Pat. No. 4,591,668, U.S. Pat. No.
2,702,354 to Creed et al., and U.S. Pat. Nos. 5,888,187 and
6,174,278 to Jaeger et al.
[0027] FIG. 2A is a side view of one embodiment of a lead that may
carry microphone 5 or another similar device for detecting sound
waves. Lead includes an elongated lead body 12 which may be formed
of silicone, polyurethane, or any other biocompatible polymer known
in the art for use in implantable devices.
[0028] Lead body 12 has a proximal end 38 adapted to be coupled to
an IMD. Proximal end may include two sets of sealing rings 22 and
24 to provide a fluid-tight seal with the IMD connector. The lead
further includes a connector pin 32 and connector ring 36. Although
the lead connector of FIG. 2 is a bipolar in-line configuration,
any other type of standard or non-standard connector type may be
utilized.
[0029] The lead body 12 has a distal end 40, which may carry a tip
electrode 26, and may also carry a ring electrode 27. Any type of
passive or active fixation mechanism may be utilized if desired,
including tines 30 or a fixation helix. Distal end 40 further
carries a microphone 5 or another similar device for detecting
sound waves.
[0030] In this embodiment, the lead body 12 carries first and
second lead conductors, which may be cabled or coiled conductors,
or any other type of configuration known in the art. During
implantation, a selectable switch is configured to couple connector
pin 32 and ring connector 36 to microphone 5 via these conductors.
When coupled to a speaker system in a manner to be discussed below,
the microphone may then be used to facilitate lead placement. After
placement has been accomplished, the switch may be reconfigured so
that connector pin 32 is coupled to tip electrode 26, and ring
connector 36 is coupled to ring electrode 27. The use of the
microphone during lead placement will be discussed in detail
below.
[0031] FIG. 2B is a side view of alternative embodiment of a lead
for use with the current invention. In this embodiment, microphone
5 is located in proximity to tip electrode 26.
[0032] FIG. 2C is an end view of yet another embodiment of a distal
end of a lead for use with the current invention. In this
embodiment, tip electrode 26a is provided with an aperture that
provides access to a recessed area that houses microphone 5.
[0033] FIG. 2D is a side cutaway view of the embodiment of FIG. 2C.
This view illustrates the manner in which the microphone 5 is
mounted within recessed area 42 to mounting structures 44. This may
be accomplished, for example, using medical grade epoxy or any
other fastening means.
[0034] Turning now to a discussion of lead placement, techniques
currently in use for permanent lead implantation typically involve
making an infraclavicular incision in the skin on either the left
or right side of the patient. The left or right subclavian vein is
punctured with a thin-walled, large-bore needle. A guidewire may
then be passed into the vein. The needle is removed and an
introducer sheath is advanced over the wire with the aid of a
dilator into the subclavian vein. After the introducer sheath is in
the subclavian vein, the dilator is withdrawn. The lead is passed
into the venous circulation system through the introducer sheath.
The guidewire may be removed or may be left in place as the lead is
passed through the system. Alternatively, a guide catheter may be
used in place of, or in addition to, a guide wire during lead
placement. The guide catheter is navigated through the venous
system to a desired implant location. Once the distal tip of the
guide catheter is in position, the lead is advanced within the
guide catheter lumen.
[0035] Regardless of the technique used, the lead may be advanced
via the superior vena cava into the right atrium and then
manipulated across the tricuspid valve into the right ventricle,
then further advanced past ventricular trabeculae to the apex of
the right ventricle to obtain an optimal pacing location in the
right ventricle.
[0036] In some instances, it is desirable to place a lead within
the coronary sinus. The coronary sinus is the largest cardiac vein
in the heart and serves as a venous conduit from smaller veins
within the myocardium to the right atrium. The coronary sinus can
be used as a location for pacing both the left and right sides of
the heart, and is often accessed to provide electrophysiology
therapy. Gaining access to the ostium of the coronary sinus is a
very difficult procedure, however, especially because of the large
number of similar anatomical structures located near the coronary
sinus within the right atrium. The location of these structures
varies from patient-to-patient, and can not be readily viewed using
a fluoroscope.
[0037] Current procedures available for introduction of leads
within the chambers of the heart as well as the venous system are
frequently time consuming and difficult. As discussed above, these
procedures may be aided by obtaining an image of the interior
anatomy of a patient. This is commonly accomplished by injecting
fluorovisible contrast media into a patient's system so that the
image may be generated by a fluoroscope. This procedure has
disadvantages, including exposing patients to the contrast media,
which may cause temporary side effects, as well as exposing
patients to radiation.
[0038] According to the current invention, an improved procedure
utilizing sound wave analysis is provided to aid in the positioning
of implantable medical devices within a patient's body. A
microphone attached to a lead captures the various sound waves
generated by a body, including sounds created by the flow of blood
through the veins and arteries, as well as the audible tones
created by atrial and ventricular contractions. The frequency and
amplitude of the sound waves vary as the microphone travels through
the body. In fact, a unique acoustic pattern or signature may be
obtained at various locations in the body. This allows a trained
user to very accurately estimate the location of a distal tip of a
lead by listening to the sounds received by a microphone carried on
the lead body.
[0039] FIG. 3 is a block diagram of a system that utilizes sound
waves to aid in the positioning of a lead within a patient's body
during an implantation procedure. This system includes lead 14,
which may be any of the embodiments shown in FIGS. 2A-2D. The
exemplary lead is similar to that shown in FIG. 2B, with similar
components being labeled with like numerical designations. This
lead is electrically and mechanically coupled to an amplifier
device 72 for amplifying sound waves received by microphone 5
located at the distal end of the lead.
[0040] In one embodiment of the invention, the lead body carries a
switch 74. This switch, which selectively couples the lead
connectors 86 and 88 to either the microphone 5 or the various lead
electrodes, may be a mechanical switch accessible to an external
surface of the lead and configured manually by a user.
Alternatively, the switch may be an electronic switch such as a
multiplexer shown in FIG. 3 that is configured by a control line
80. Control line 80 is coupled via an additional connector ring 82
at the proximal end of lead 14 to resistor network 84 within
amplifier device 72, and is thereby maintained at an appropriate
voltage level, which in this instance is shown to be ground.
[0041] Before an implantation procedure is initiated, the lead
proximal end is coupled to the amplifier device 72 and switch 74 is
configured so that conductors 90 and 92 couple microphone 5 to pin
connector 32 and ring connector 36, respectively, of the lead via
conductors 86 and 88. As discussed above, if switch 74 is a
multiplexer, switch configuration will occur automatically when
control line 80 is pulled to a predetermined voltage level after
being coupled to amplifier device 72.
[0042] After the switch is configured, the lead distal tip is
introduced into the patient's body. Placement of the lead may be
aided by a guidewire and/or guide catheter. As the distal tip 40 of
lead 14 is navigated through the venous system and heart chambers,
sound waves 90 are received by microphone 5. The microphone
converts the sound waves to an electrical signal, which is
transmitted between conductors 90 and 92 to conductors 86 and 88,
and finally to the pin connector 32 and ring connector 36 of the
lead. This signal is electrically transmitted via conductors within
amplifier device 72 to preamplifier circuit 100. Pre-amplifier
circuit amplifies the electrical signal, which is then provided to
filter 102. Filter 102 eliminates noise from the signal. A filter
for use with the current invention will be selected to pass signals
having a frequency within a predetermined portion of the audio
range. The filter may be adjustable using tuning circuitry 104,
which selects the retained range of frequencies.
[0043] The filtered signal is provided to amplifier circuit 106,
which may have an adjustable gain that is controlled by gain
adjustment circuitry 108. The amplified signal is provided to
speaker 110. Speaker generates an audible signal indicative of
sound waves 90 as controlled by volume control 112. To a trained
ear, the audible signal will distinctly indicate the position of
the microphone within the body so that lead placement can be
facilitated more easily. For example, direct contact of a valve
leaflet with an endocardial microphone will produce a distinct
acoustic pattern identifiable by the user. The audible signal can
be used to locate the coronary sinus ostium, or to pin-point lead
distal tip location within an atrial or ventricular chamber of the
heart. Moreover, the extent of lead fixation at the distal tip can
be determined by a change in audible signal as a fixation mechanism
such as tines 30 are embedded within the heart wall. The audible
tones can also be used to detect lead dislodgement, as may occur
when a guide catheter is removed from the body after lead placement
has been completed. Furthermore, these tones can be used for
long-term monitoring and diagnostic purposes. For example, audible
tones will change with the accumulation of fluid in the patient's
system, as generally occurs when a patient becomes ischemic. This
tonal change can be used to detect the on-set of such conditions so
that appropriate therapy may be provided.
[0044] In one embodiment of the invention, the signal generated by
amplifier circuit 106 is provided to an analog-to-digital (A/D)
converter 120. The digital signal may be stored in Random Access
Memory (RAM) 122, or received directly by processing circuit 124.
Processing circuit 124, under the control of microcode stored in
RAM 122 and/or Read-Only Memory (ROM) 126, may compare the
digitized audio signals to audio signatures stored in RAM and/or
ROM. These stored signatures may represent typical audio signatures
at various locations in a patient's body. Based on this comparison
between the measured audio signals and the stored signatures, an
approximate location of microphone 5 within the body may be
determined. This approximate location data can be provided to an
output device 130 for use by the clinician. Output device 130 of
FIG. 3 is shown to be a display which generates a virtual image of
the approximate location of the microphone 5, as well as the rest
of lead 14. Alternatively, the processing circuit 124 may provide
the location information to another type of output device, such as
a printer, an LED display, or any other type of user interface.
[0045] The audio signatures used for comparison purposes may vary
from patient to patient based on physiological characteristics,
including a patient's size, weight, health conditions, and so on.
Therefore, in one embodiment of the invention, these signatures can
be selected based on these characteristics. The selected signatures
may be downloaded to RAM prior to initiation of the implant
procedure. In another embodiment, audio signatures may be obtained
directly from a patient during a previously-completed mapping
procedure. In such a procedure, the position of an implanted
flouro-visible microphone is varied within the patient's body. The
audio signature is recorded at each location within the body. At
the same time, the precise location as determined by a flouroscope
is also stored along with the corresponding signature. This audio
map may be stored in a patient profile and downloaded to amplifier
device 72 during any subsequent implant procedure to accurately
place a lead or another implantable device.
[0046] It may be appreciated that many different embodiments of
amplifier device 72 are possible within the scope of the current
invention. For example, pre-amplifier circuit 100 may not be
included in some embodiments. In other embodiments, the speaker 1
10 and/or volume control may be provided as a separate device.
Similarly, optional display 130 may be incorporated into amplifier
device 72, or may be omitted entirely from the system.
Alternatively, the processing circuit 124, A/D converter 120, and
memory may be provided along with display 130 as a separate device
or omitted entirely.
[0047] Further, it may be appreciated that many alternative
embodiments of the lead system may be used with the current
invention. For example, if additional connectors are provided on
the lead proximal end so that dedicated connectors are available
for transmitting the signal received from the microphone 5, switch
74 may be omitted. Additionally, the lead may include more or fewer
electrodes.
[0048] FIG. 4 is a block diagram of an implantable medical device
(IMD) as may be used with the current invention. IMD may be of any
type of implantable device known in the art, including any of those
discussed above. The exemplary device shown in FIG. 4 is pacemaker
11 electrically coupled to patient's heart 16 by lead 14.
Stimulation may be provided to heart 16 via output circuit 144
under the control of digital controller/timer circuit 134.
Similarly, cardiac signals may be sensed by EGM amplifier circuit
146. Controller/timer circuit 134 also provides a control line 136
to control the configuration of switch 74 (FIG. 3) carried by lead
14 in a manner to be discussed below.
[0049] IMD 11 further includes microcomputer unit 118. This unit
may include on-board circuit 125 comprising microprocessor 123,
system clock 122, and on-board RAM 124 and ROM 126. In this
illustrative embodiment, an off-board circuit 128 comprises a
RAM/ROM unit. On-board circuit 125 and off-board circuit 128 are
each coupled by a data communication bus 130 to digital
controller/timer circuit 134. Electrical components are powered by
an appropriate implantable battery power source 164 in accordance
with common practice in the art. Antenna 156 is connected to
input/output circuit 132 to permit uplink/downlink telemetry with
an external device through RF transmitter and receiver unit 154.
Transmitter/Receiver unit 154 may correspond to the telemetry and
program logic disclosed in U.S. Pat. No 4,566,063 issued to
Thompson et al. Voltage reference (VREF) and bias circuit 160
generates a stable voltage reference and bias current for the
analog circuits of input/output circuit 132. Analog-to-digital
converter (ADC) and multiplexer unit 158 digitize analog signals
and voltages to provide "real-time" intracardiac signals and
battery end-of-life (EOL) replacement signals that may be stored in
memory or transmitted to an external device such as a
programmer.
[0050] Operating commands for controlling the timing of pacemaker
11 are coupled by data bus 130 to digital controller/timer circuit
134, where digital timers and counters establish the overall escape
interval of the pacemaker as well as various refractory, blanking,
and other timing windows for controlling the operation of the
peripheral components disposed within input/output circuit 132.
[0051] As discussed above, in addition to providing timing and
control signals that control the delivery of therapy, digital
controller/timer circuit 134 also provides a control signal on line
200 that configures switch 74 (FIG. 3.) During normal operation,
switch is configured via the signal on line 136 so that electrodes
carried by lead 14 are coupled to input/output circuit 132 in the
manner discussed above. However, during periodic intervals, switch
74 may be temporarily configured by changing the voltage level on
signal line 136 so that microphone 5 is coupled electrically to
sense amplifier 142. Acoustic signals sensed by microphone 5 are
amplified and/or filtered by circuit 141 and provided to
controller/timer circuit 134. These signals may be digitized by ADC
circuit 158, and thereafter stored in RAM 124 or RAM/ROM unit 128.
The processor may compare these signals to stored audio patterns or
signatures to determine whether lead dislodgment has occurred. If
such dislodgment is detected, an audible alert may be generated, or
a warning message may be transmitted via RF transmitter/receiver
circuit 154.
[0052] As discussed above, changes in the audio signals can also be
used to detect a change in a patient's long-term condition.
Digitized audio signals may be periodically stored in memory to
diagnose trends. Changes over time may signal such conditions as
the on-set of ischemia, for example. If such conditions are
detected, a warning may be provided so that appropriate therapy may
be prescribed and delivered. Alternatively, a therapy may be
automatically administered by changing the pacing regimen, for
example.
[0053] Although the foregoing example discusses the use of a
bipolar medical electrical lead, many other embodiments of the
system are possible. For example, a microphone may be included in a
drug delivery catheter, a guide catheter, a stylet, a guidewire, a
unipolar lead, a lead for providing electrical stimulation to the
nervous system, or any other type of implantable device that is
navigated into position within a patient's body.
[0054] FIG. 5A is a side view of an exemplary deflectable guide
catheter 200 that may usefully employ the current invention. This
guide catheter is described in detail in commonly-assigned U.S.
Pat. No. 6,006,137 incorporated herein by reference in its
entirety. It will be understood that this catheter design is merely
exemplary, and any other deflectable or non-deflectable catheter
design may usefully employ the current invention. This exemplary
guide catheter has an elongated body 202 and a deflectable distal
tip 206 controlled by several internal deflection wires coupled to
two rotatable knobs 201 and 203. A medical electrical lead 204 is
shown being advanced within an internal lumen of the guide
catheter. The distal tip further carries a microphone 210 or
another similar instrument for measuring sound waves. The proximal
end of the guide catheter includes a connector 212 that can be
coupled to amplifier device 72 in the manner discussed above.
Acoustic waves received by microphone 210 can thereby be used to
place the distal tip of the guide catheter so that a lead may be
delivered at a predetermined location.
[0055] FIG. 5B is a perspective view of an exemplary steerable
stylet and manipulative handle assembly 300 as may be employed with
the current invention. This stylet assembly is described in
commonly-assigned U.S. Pat. No. 5,396,902 incorporated herein by
reference. It will be understood that this stylet design is merely
exemplary, and any other deflectable or non-deflectable stylet
design may usefully employ the current invention. This style has a
deflectable distal end 316 shaped via movement of pull wire 312 in
relation to the elongated tubular member 310. In use, tubular
member 310 and pull wire 312 are inserted into connector pin
opening of a lead or catheter (not shown) and advanced into an
inner lumen of the device. After this mechanical connection is
effected, the lead or catheter may be rotated by rotation of
housing 330, and curvature may be imparted by slide member 320
acting on pull wire 312. Distal tip of the stylet includes a
microphone 340 to detect sound waves, which are converted to an
electrical signal. Connector 350 is provided to couple to a device
such as amplifier device 72 in a manner to discussed above so that
the distal end of the stylet may be accurately positioned within
the body.
[0056] The foregoing discussion focuses on the use of acoustic
information to aid in determining location and/or tissue contact of
an implantable device. Other types of sensors such as sensor 15
(FIG. 1) may be employed to gather additional information that may
be used in conjunction with audio signal data to even more
accurately determine the location of an IMD. For example, pressure
data may be utilized to determine location of a pressure sensor.
This is possible because intravascular pressure varies by location
within the body in a manner similar to that discussed above with
audible signals. For example, a distinct pressure shift may be
detected as a pressure sensor enters the coronary sinus. Other
pressure shifts occur as a sensor is moved from one cardiac chamber
to the next. Therefore, a pressure sensor coupled to an IMD may be
used to transfer signals to a device such as amplifier device 72
(FIG. 3). These signals may be digitized by A/D converter 120 and
compared by processing circuit 124 to pressure signatures stored in
RAM 122 or ROM 126 for use in determining the approximate the
location of the pressure sensor in the body. This approximation may
be used in conjunction with the analysis of the audio signals
discussed above to even more accurately determine the location of
the IMD. The sensor data may also be displayed on one or more
output devices, as described above.
[0057] Any type of implantable pressure sensor may be adapted for
use with the current invention. For example, commonly assigned U.S.
Pat. No. 5,564,434 discloses an endocardial lead having a sensor to
provide modulated pressure signals to an external monitor.
Additional exemplary pressure sensing systems are disclosed in U.S.
Pat. Nos. 5,526,820, 4,924,877, 5,427,144, and 5,348,019.
[0058] Other types of sensor data may be used in a manner similar
to the pressure signals to further pin-point the location of an
IMD. For example, sensors to measure flow velocities may be
utilized to further determine location. Systems of this nature are
discussed in U.S. Pat. Nos. 4,947,852, 5,078,148, 5,333,614, and
5,873,835. Another physiological parameter that may be used in
conjunction with the current invention includes acceleration of
blood flow, measurement of which is discussed in U.S. Pat. No.
4,608,993. Velocity and direction of electrical activity within
myocardial tissue may also be measured to determine location, as
discussed in U.S. Pat. No. 6,064,905.
[0059] FIG. 6 is a flowchart of an exemplary process of positioning
an implantable medical device according to the current invention.
The system is first configured to receive acoustic data (400). This
may involve setting a switch to a predetermined setting and/or
connecting the IMD to the amplifier device. It may further involve
loading acoustic pattern data into the amplifier device so that the
acoustic analysis is tailored to an individual patient in the
manner discussed above. Acoustic data may then be received by an
acoustic measurement device such as a microphone (402). An
electrical representation of the sensed acoustic data is filtered
(404) and amplified (406). An audible signal may then be generated
for use by a trained practitioner in determining position of the
acoustic measuring device within a body (408).
[0060] Optionally, the filtered and amplified signal may be
digitized (410) and compared to stored acoustic patterns as may be
accomplished by a processing circuit under the control of
microcode, for example (412). As noted above, the stored acoustic
patterns may be tailored to reflect individual patient
characteristics. Using the results of the comparison, status
associated with the IMD may be determined (414). This status may
include the approximate location of the acoustic measurement device
within the body, as well as the extent of any contact between
tissue and the acoustic measurement device.
[0061] If desired, one or more additional sensors such as sensor 15
(FIG. 1) may be utilized to obtain additional physiological
measurements including pressure, blood flow velocity and
acceleration, and the velocity and direction of electrical activity
in myocardial tissue (416). These measurements may be received by
amplifier device 72 and processed in a manner similar to that
described above with respect to audio signals. For example, these
signals may be filtered, amplified, and digitized. The digital
signals may then be compared to pattern data stored in memory
(418). The results of this comparison are used to even more
accurately determine the status of an IMD, including IMD location
(420). After the IMD status including location data is determined,
the information is provided to a user. (422) For example, an image
of the approximate location may be generated on a display device,
or a printer may be utilized to provide the position
information.
[0062] It may be noted that the ordering of the steps of FIG. 6 is
in some cases arbitrary. For example, the order of filtering and
amplification steps 404 and 406 may be reversed. Step 408 may be
omitted, or alternatively, any of steps 410 through 422 may be
omitted. Therefore, it will be understood that FIG. 6 is exemplary
in nature, rather than limiting.
[0063] FIG. 7 is a flowchart of an exemplary process of utilizing
the current invention to monitor long-term status of system such as
a pacemaker coupled to one or more leads implanted within a
patient. An exemplary system is shown in FIG. 4. According to this
method of use, the system is configured to receive acoustic signals
(440). This may involve configuring a switch such as switch 74 so
that acoustic signals may be received by the pacemaker. After
system configuration is completed, the acoustic data may be
obtained using an acoustic sensing device such as a microphone.
Optionally, other physiological data may also be obtained from one
or more additional sensors such as a temperature, pressure, or any
other sensor of a type known in the art (442).
[0064] After the acoustic and any other additional signal data is
obtained, this data may be filtered and amplified (444). This data
may further be digitized and sampled so that it may be stored in a
storage device within the pacemaker (146). The sampled data may be
analyzed by a processing circuit such as microprocessor 123 (148).
This evaluation process may involve a rules-based analysis, and/or
a comparison to stored pattern data, for example. After the
analysis is complete, one or more additional actions may be taken
(152). For instance, a warning may be generated to indicate the
dislodgement of a lead or detachment of a fixation mechanism.
Alternatively, the warning may indicate a worsening patient
condition. This warning may be an audible alert, or may involve
up-loading data to an external device such as a programmer. In one
embodiment, the detection of a patient condition may result in the
initiation or modification of therapy delivery by the pacemaker or
other IMD.
[0065] The above embodiments will be understood to be exemplary
only. Those skilled in the art may contemplate variations within
the scope of the present invention. The scope of the invention is
therefore to be limited only in reference to the claims that
follow.
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